The present invention relates to a sliding-treated gasket. In particular, it is an invention suitable for a fuel cap gasket.
Herein, the present invention is explained by exemplifying a fuel cap gasket, being not limiting.
Abbreviations of main polymers and reagents used in the present invention are as follows:    NBR . . . nitrile rubber    PVC . . . polyvinyl chloride    FKM . . . fluorine rubber.
Conventionaly, a material for a fuel cap gasket was mainly a polyblend of NBR/PVC because when PVC is blended with NBR, the resistance to weather, the resistance to ozone, the resistance to oil, the resistance to chemicals and the resistance to abrasion are improved (“Revised and enlarged New Edition Synthetic Rubber Handbook” (Nov. 30, 1967) Asakurashoten, P.662).
And, as shown in FIG. 1, it is necessary to open and close a fuel cap 12 every oil feeding. Upon this, a gasket 14 mounted on a cap 12 is slided with a seal bearing surface 10a of a filler neck 10. For this reason, it is required to have the better sliding property.
Therefore, previously, chlorinating treatment was performed in order to enhance the sliding property of a gasket 14.
Specifically, a rubber was reacted with chlorine freed by dissolving a chlorine compound (e.g. trichloroisocyanuric acid) in water.
On the other hand, from a viewpoint of the environmental problem, it has been required that an amount of gasoline permeating from an oil feeding port, that is, a fuel cap is smaller than previous (e.g. Fuel Permeation Regulation in North America Act).
However, since a polyblend of NBR/PVC can not cope with the requirement, it can be contemplated that a fuel cap is formed of a fluorine-based rubber (FKM) having the excellent resistance to gasoline permeability.
However, since even FKM is not sufficient in the sliding property like the case of NBR/PVC, it is necessary to perform sliding treatment. However, the chlorinating treatment (the sliding treatment) as in NBR/PVC is impossible to apply to FKM.
Then, the present inventors coated (scattered) a solid lubricant such as molybdenum disulfide (MOS2) and the like, but it was found that the lubricant is peeled after a durability test (e.g. fasten/unfasten 3000 times), and the sliding property cannot be maintained for a long period of time.
Although the inventiveness of the present invention is not influenced, there are following publications as the related prior art exhibiting the technical status.
JP-A 11-255929: A surface treating agent containing a phosphorus compounding agent was coated on the surface of a fluorine rubber after primary vulcanization, and this was dried and heated to form a surface-treated layer and, at the same time, after secondary vulcanization, a fluorine resin was coated thereon to maintain the adherability of a coating layer.
JP-A 2000-337515: By covering an elastic layer (e.g. FKM rubber) of a gasket with a harder covering layer (e.g. fluorine resin) than the elastic layer, creep and flowing at pressing are prevented.